In a typical rail vehicle application, for example, locomotives in a consist, the on-board clock of the rail vehicle control system (e.g., CMU or communication management unit) is synchronized, for example, to an off-board clock when the rail vehicle is first initialized or powered up, but not during ongoing operation. In other words, while the on-board clock is synched initially, upon vehicle start-up, it is not synched thereafter during vehicle operation. As will be readily appreciated, the reason for not regularly synching the on-board clock subsequent to initialization is to maintain a consistent clock during vehicle operation, which is necessary for the precise operation of various systems on-board the rail vehicle, such as an event recorder. More specifically, with respect to the event recorder, a continuous time stream without any discontinuities is desired. If the on-board clock was re-synched during vehicle operation, discontinuities may manifest, which could disrupt the precise operation of the event recorder and other systems relying on the on-board clock.
With existing rail vehicles such as locomotives, because the CMU on-board clock is only synched upon vehicle initialization/start-up, the CMU clock may drift from off-board clocks. In a train with multiple locomotives, the CMU clock may also drift from the clocks of other locomotives. In certain systems, the time discrepancies between the CMU clock and an off-board clock, or the CMU clock and the clocks of other locomotives in the consist, can, however, be problematic. For example, for a vehicle control system where an on-board control system, such as an energy management system, works in conjunction with an off-board scheduler, if the clock of the on-board system doesn't match (i.e., isn't synched) the clock of the off-board system, accurate vehicle control cannot be achieved. For example, if the off-board system tells the on-board system that the train should be at a particular location at a particular time, and the clocks do not match, than the train may not be at the location at the correct time.
Accordingly, there is a need for a method and system for synchronizing the on-board clock of a rail vehicle with other clocks, including an off-board clock and/or the clocks on-board other rail vehicles in the consist.